The present invention relates to methods and apparatus for manufacturing helically coiled continuous coupling elements for a slide fastener.
There have been employed various bobbins for storing an element-forming filamentary material which is unwound as it is fed to and formed by a mandrel into a helical coil structure suitable for a slide fastener. From the standpoint of providing a sufficient inventory of filaments per bobbin to dispense with their frequent replacement during operation and to produce a substantially endless or uninterrupted length of fastener element, it is desirable to use literally large bobbins. However, it has been found extremely difficult to use large capacity bobbins with most prior art apparatus for reasons hereafter set forth. One conventional apparatus included bobbins which are nonrotatably set in place. Although a greater supply of element-forming filament could be achieved simply by increasing the capacity of such nonrotatable bobbin, the filament was prone to get twisted as each individual convolution is formed or otherwise deformed when unwound from the bobbin on account of the latter being held stationarily in place with the results that such surface defects appear in the convolutions of the resulting coiled element. This would further result in deformed coupling heads of the elements and also adversely affect the shape and dimensions of the finished fastener element.
Another prior art apparatus employed a bobbin which is rotatable about the axis of the mandrel in order to remove twists on the filament. According to this proposal, the filament was unwound from the bobbin through a filament guide rotor which rotates synchronously with a guide member on a filament coiling machine. Since the bobbin was rotated at higher speeds than the rotor as the filament was fed, the filament was subjected to irregular tension due to changing inventory of the filament on the bobbin, and hence it became necessary to install additional devices for compensating for such irregular filament tension. This prior art proposal was further complicated by the provision of a suitable device for preventing the filament from being excessively taut at the start of operation of the apparatus. According to still another conventional apparatus, a rotatable type of bobbin is provided substantially at right angles to and arranged to move around the mandrel during withdrawal of the filament. This apparatus however has suffered not only from the above-noted difficulties but also the problem that the use of larger bobbins is prohibited due primarily to excessive centrifugal forces generated by their rotation around the mandrel.